Object information acquiring apparatus and control method thereof

ABSTRACT

Provided is an object information acquiring apparatus, including: a light source; a detecting unit that detects an acoustic wave generated from an object which has received an irradiation light from the light source; a processing unit that generates characteristic information on the inside of the object by using the acoustic wave; and a memory unit that records the characteristic information in association with information on the irradiation light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/405,274, filed on Dec. 3, 2014, which is a national stage entry ofPCT/JP2013/068190, filed Jun. 26, 2013, which claims the benefit ofpriority from Japanese Application No. 2012-158988 filed Jul. 17, 2012.The contents of the aforementioned applications are incorporated hereinby reference in their entireties.

TECHNICAL FIELD

The present invention relates to an object information acquiringapparatus and a control method thereof.

BACKGROUND ART

Research on optical imaging techniques is ongoing in medical fields toacquire information on the inside of an object by irradiating light ontothe object, and PAT (Photoacoustic Tomography) is one of thesetechniques. PAT utilizes the photoacoustic effect when a light absorber(a region having a high absorption coefficient) in the object absorbsenergy of the irradiated light, expands its volume, generates aphotoacoustic wave, and visualizes information related to the opticalcharacteristic values inside the object. To visualize information, anacoustic wave is detected at a plurality of locations surrounding theobject, and acquired signals are mathematically analyzed.

If a photoacoustic diagnostic apparatus based on the PAT technique isused, such information as initial sound pressure distribution and lightenergy absorption density distribution inside the object can beacquired, and the acquired information can be used for specifying alocation of a malignant tumor that involves the growth of new bloodvessels, for example. In the following, the description on initial soundpressure distribution includes description on light energy absorptiondensity. Generating and displaying a three-dimensional reconstructedimage based on such initial sound pressure distribution is useful inknowing the internal state of biological tissue for diagnosis.

On the other hand, along with the recent advancements of informationprocessors and the increase in data capacity, three-dimensional imagesof the human body, such as CT and MRI, are used at higher frequencies inthe medical field. For medical image diagnosis, it is desirable to saveall the data for a long period of time in order to compare the testresults of a plurality of modalities, and observe progress aftersurgery. However three-dimensional image data normally has largecapacity, and redundant data must be minimized for long term datastorage.

For the format of three-dimensional image data, a standard format, suchas volume data format, is better than an application-specific format interms of versatility which allows the use of various software, and easydata analysis. Therefore in a photoacoustic diagnostic apparatus aswell, it is preferable to output a three-dimensional image in volumedata format.

Now the characteristics of a reconstructed image by PAT will bedescribed. In the case of PAT, if the time variation of an acoustic waveis measured at various points on a closed spatial surface (a sphericalmeasurement surface in particular) that surrounds the entire object,using an ideal acoustic detector (wideband, point detection), theinitial sound pressure distribution generated by photo-irradiation cantheoretically be completely visualized. It is also known that theinitial sound pressure distribution generated by photo-irradiation canbe reproduced almost perfectly if columnar or planar measurement isperformed on the object, even if a closed space is not used (see NPL 1).

Expression (1) is a partial differential equation called a“photoacoustic wave equation”, and by solving this equation, acousticwave propagation from the initial sound pressure distribution can bedescribed, and where and how the acoustic wave could be detected can betheoretically performed.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack & \; \\{{\left( {{\nabla^{2}{- \frac{1}{c^{2}}}}\frac{\partial^{2}}{\partial t^{2}}} \right){p\left( {r,t} \right)}} = {{- {p_{0}(r)}}\frac{\partial{\delta(t)}}{\partial t}}} & (1)\end{matrix}$where r denotes a position, t denotes time, p(r, t) denotes timevariation of the sound pressure, p₀(r) denotes initial sound pressuredistribution, and c denotes sound velocity. δ(t) denotes a deltafunction that represents the shape of the light pulse.

Reconstructing an image by PAT means deriving the initial sound pressuredistribution p₀(r) from the sound pressure pd (r_(d),t) acquired at adetection point, which in mathematics is called an “inverse problem”.The UBP (Universal Back Projection) method, which is a representativeimage reconstruction method based on PAT, will now be described. Theinverse problem to determine p₀(r) can be accurately solved by analyzingthe photoacoustic wave equation of Expression (1) in the frequencyspace. UBP is this result expressed in the time space. FinallyExpression (2) shown below is derived.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack & \; \\{{p_{0}(r)} = {{- \frac{2}{\Omega_{0}}}{\nabla{\cdot {\int_{S_{0}}^{\;}{{\overset{\Cap}{n}\ }_{0}^{S}{{dS}_{0}\left\lbrack \frac{p_{0}\left( {r_{0},t} \right)}{t} \right\rbrack}_{t = {{r - r_{0}}}}}}}}}} & (2)\end{matrix}$where Ω₀ denotes a solid angle of the entire measurement area S₀ at anarbitrary voxel (unit region).

This expression can be simplified and transformed into Expression (3)shown below.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 3} \right\rbrack & \; \\{{p_{0}(r)} = {\int_{\Omega_{0}}^{\;}{{b\left( {r_{0},{t = \ {{r - r_{0}}}}} \right)}\frac{d\;\Omega_{0}}{\Omega_{0}}}}} & (3)\end{matrix}$where b(r₀,t) denotes projection data, and dΩ₀ denotes a solid angle ofa detector dS₀ to an arbitrary observation point P. The initial soundpressure distribution p₀(r) can be acquired by performing backprojection of this projection data according to the integration ofExpression (3).

b(r₀,t) and dΩ₀ are given by Expression (4) and Expression (5) shownbelow.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 4} \right\rbrack & \; \\{{b\left( {r_{0},t} \right)} = {{2{p\left( {r_{0},t} \right)}} - {2t\frac{\partial{p\left( {r_{0},t} \right)}}{\partial t}}}} & (4) \\{{d\;\Omega_{0}} = {\frac{d\; S_{0}}{\ {{r - r_{0}}}^{2}}\cos\;\theta}} & (5)\end{matrix}$where θ is an angle formed by the detector and an arbitrary observationpoint P.

If the distance between the sound source and the measurement position issufficiently long with respect to the level of the sound source (longdistance sound field approximation), Expression (6) shown below is used.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 5} \right\rbrack & \; \\{{p\left( {r_{0},t} \right)}{\operatorname{<<}\; t}\frac{\partial{p\left( {r_{0},t} \right)}}{\partial t}} & (6)\end{matrix}$

In this case, b(r₀,t) is given by Expression (7) shown below.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 6} \right\rbrack & \; \\{{b\left( {r_{0},t} \right)} = {{- 2}t\frac{\partial{p\left( {r_{0},t} \right)}}{\partial t}}} & (7)\end{matrix}$

Thus in the image reconstruction based on PAT, the projection datab(r₀,t) is determined by time-differentiating the detection signalp(r₀,t) acquired by the detector, and is back-projected according toExpression (3), whereby the initial sound pressure distribution p₀(r) isdetermined (see NPL 1).

Expression (1), used for determining Expression (3), however, assumes“constant sound velocity”, “measurement from every direction”, “impulsetype photo-excitation”, “acoustic wave detection in broadband”,“acoustic wave detection at a point” and “continuous acoustic wavesampling”. In reality it is not easy to implement an apparatus thatsatisfies these assumptions.

For example, it is actually difficult to acquire acoustic wave detectioninformation on the total closed spatial surface surrounding the entireobject. Furthermore, in order to increase the acoustic wave measurementregion, the size and number of elements of the acoustic detector, and asignal processing unit and control unit of each element must beincreased, which increases manufacturing cost. For these reasons manypractical measurement apparatuses based on the PAT technique detect anacoustic wave from an object in a specific direction using a limitedsized probe.

An example of such an apparatus is the PAT of a plate type measurementsystem disclosed in PTL 1. According to PTL 1, light is irradiated ontoan object sandwiched by plates, and an acoustic wave is detected by anacoustic wave detector installed on the plate. In some cases the lightis irradiated and the acoustic wave is detected for a plurality oftimes, and measured values are averaged, whereby such an effect as animprovement in the S/N ratio is implemented.

Image qualities (S/N ratio, artifact) of a reconstructed image in aphotoacoustic diagnostic apparatus are influenced not only by the abovementioned acoustic wave detection conditions, but also by lightirradiation conditions. If light is irradiated from outside an object,the level of light decays from the surface area to a deep part of theobject due to the absorption of light by biological tissue. In effect itis difficult to irradiate light onto an object under ideal conditions.

It is possible to estimate the intensity of the irradiated light insidethe object. In other words, the extent of decay of the level ofirradiated light is determined considering an absorption coefficientaccording to a segment of the object, and light energy distribution isestimated. However it is difficult to completely eliminate the artifactsand errors of signal values even if the signal values of thephotoacoustic wave are corrected based on the estimation result.

Furthermore, data becomes enormous if all factors that could influencethe optical system in the imaging apparatus are recorded for the object.In the case of a method of recording and simulating the specificationsand settings of each apparatus, the recording method and utilizationmethod could be overly specific. It also involves complicated handlingand time to calculate information on the irradiated light from therecorded data.

In the case of using a reconstructed image of the photoacousticdiagnostic apparatus for the purpose of medical diagnosis, it isnecessary to know the degree of reliability and the influence of opticalconditions within a reconstructed image. However conventionallyphoto-irradiation conditions depend on the design and specifications ofthe apparatus, and are recorded as apparatus-dependent information (e.g.setting values and imaging conditions of the apparatus). It is also timeconsuming to analyze information when conditions of the irradiated lightare reproduced based on the recorded information. In photoacousticdiagnostic apparatuses as well, no technique is available to storeinformation on individual irradiated light for each reconstructed image.

According to the technique disclosed in PTL 2, virtual light sourceinformation is stored to render computer graphics for creating athree-dimensional image. However information on irradiated light forimaging inside biological tissue cannot be stored as informationcorresponding to the reconstructed image. Therefore the only way todisplay and analyze a reconstructed image considering the conditions ofirradiated light is to record redundant data which depends on theapparatus, and to perform time consuming analysis processing.

CITATION LIST Patent Literature

-   PTL 1: US Patent Description No. 5840023-   PTL 2: Japanese Patent Application Laid-Open No. 2006-023820

Non Patent Literature

-   NPL 1: Physical Review E 71, 016706 (2005)

SUMMARY OF INVENTION Technical Problem

In the case of imaging by the photoacoustic diagnostic apparatus,scattering and decaying of transmitted light occur inside the object,and a tendency of the scattering and decaying depends on the region ofthe object, and is not uniform (particularly in a shallow region nearthe irradiation surface). Therefore conditions of generating aphotoacoustic wave differ depending on the region, even within thevolume data acquired by reconstruction. It is also difficult tocompletely clear artifacts generated under various conditions related tophoto-irradiation and acoustic wave acquisition, and to completely clearerrors of calculated values from the three-dimensional reconstructedimage in which the initial sound pressure distribution in the object isgenerated.

In order to reconstruct a good image under these conditions, it isnecessary to estimate the quantity of light at each location in theobject, and store the information on the irradiated light along with thereconstructed image as data for estimating the quantity of light.However the use of redundant data and an enormous amount of efforts arerequired to display and analyze the reconstructed image, since notechnique is available to record information on the irradiated lightduring imaging in a standard and versatile format without using a formatthat depends on the measurement apparatus.

With the foregoing in view, it is an object of the present invention torecord information on the irradiated light used in photoacoustictomography in correspondence with the reconstructed image, so that theinformation can be easily used for displaying and analyzing thereconstructed image.

Solution to Problem

The present invention provides an object information acquiringapparatus, comprising:

a light source;

a detecting unit configured to detect an acoustic wave generated from anobject which has received an irradiation light from the light source;

a processing unit configured to generate characteristic information onthe inside of the object by using the acoustic wave; and

a memory unit configured to record the characteristic information inassociation with information on the irradiation light.

The present invention also provides a method for controlling an objectinformation acquiring apparatus, comprising:

a step of emitting an irradiation light from a light source to anobject;

a step of detecting an acoustic wave generated from the object which hasreceived the irradiation light;

a step of generating characteristic information on the inside of theobject by using the acoustic wave; and

a step of storing the characteristic information in association with theinformation on the irradiation light.

Advantageous Effects of Invention

According to the present invention, information on the irradiated lightused in photoacoustic tomography can be recorded in correspondence withthe reconstructed image, so that the information can be easily used fordisplaying and analyzing the reconstructed image.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram depicting functional blocks of a photoacousticdiagnostic apparatus;

FIG. 2 is a diagram depicting a configuration example of an informationprocessing unit;

FIG. 3 is a diagram depicting a configuration example of a photoacousticwave signal measuring unit;

FIG. 4 is a flow chart depicting a processing procedure from startingimaging to instructing acquisition;

FIG. 5 is a diagram depicting a relationship between an object, animaging region and an irradiated light;

FIG. 6 is a flow chart depicting a processing procedure to acquire aphotoacoustic wave signal;

FIG. 7 is a diagram depicting a relationship between an object, a smallimaging region and irradiated light;

FIG. 8 is a flow chart depicting a procedure to convert and storeinformation on an irradiated light;

FIG. 9 is a diagram depicting an irradiated light for a smallreconstruction region;

FIG. 10 is a diagram depicting an irradiated light for a largereconstruction region;

FIG. 11 is a diagram depicting simplified information on an irradiatedlight for a reconstruction region; and

FIG. 12 is a flow chart depicting a procedure to use information on thestored irradiated light.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the drawings. Dimensions, materials, shapes andrelative positional relationships of the components described belowcould be appropriately modified according to the configuration andvarious conditions of the apparatus to which the present invention isapplied, and are not intended to limit the scope of the invention.

An object information acquiring apparatus of the present inventionincludes an apparatus that receives an acoustic wave (typically anultrasonic wave) generated inside an object by irradiating light(electromagnetic wave) onto the object, and acquires the objectinformation distribution as image data.

In the case of an apparatus using the photoacoustic effect, objectinformation is a generation source distribution of an acoustic wavegenerated by the photo-irradiation, an initial sound pressuredistribution in the object, a light energy absorption densitydistribution derived from the initial sound pressure distribution, anabsorption coefficient distribution, and a concentration informationdistribution of a substance constituting a tissue. The densityinformation distribution of a substance is, for example, an oxygensaturation distribution or an oxygenated/deoxygenated hemoglobinconcentration distribution. This characteristic information is called“object information”.

The acoustic wave according to the present invention is a compressionalwave, and includes an elastic wave called a “sound wave”, an “ultrasonicwave” and an “acoustic wave”. An example is an acoustic wave that isgenerated inside an object when a near-infrared ray is irradiated insidethe object. An acoustic wave generated by the photoacoustic effect iscalled a “photoacoustic wave” or a “photoacoustic ultrasonic wave”. Anacoustic detector (e.g. probe) receives an acoustic wave generated inthe object.

Embodiments

A photoacoustic diagnostic apparatus according to an embodiment detectsan acoustic wave which is generated by irradiating light onto an object,and generates a three-dimensional reconstructed image. In thisembodiment, by one imaging process, information on the irradiated lightthat can be used for a coordinate system, which is relatively determinedfor an imaging region, is generated along with the detected acousticwave signal. Furthermore, the information on the coordinate system andthe irradiated light is stored as recording data, so that informationbased on volume data of the reconstructed image can be easily displayedand analyzed.

(Functional Block Diagram)

FIG. 1 shows the functional blocks of the photoacoustic diagnosticapparatus. The photoacoustic diagnostic apparatus is comprised of aninformation processing unit 1000 and an acoustic wave signal measuringunit 1100. FIG. 2 and FIG. 3 show an example of the apparatusconfiguration to implement each functional block. FIG. 2 is an exampleof the apparatus configuration to implement the information processingunit 1000. FIG. 3 is an example of the apparatus configuration toimplement the photoacoustic wave signal measuring unit 1100.

The photoacoustic wave signal measuring unit 1100 measures an acousticwave signal. The photoacoustic wave signal measuring unit 1100 controlsacoustic wave measurement based on the acoustic wave measurement methodinstructed from the information processing unit 1000, generatesphotoacoustic wave signal information based on an acoustic wave detectedby each element of an acoustic wave detector 1105, and transmits thephotoacoustic wave signal information to the information processing unit1000.

Here the acoustic wave detector 1105 is a probe to detect an acousticwave, for example. The photoacoustic wave signal information correspondsto information of the receiving element, such as an acoustic wave signaldetected by an element of the probe, information on the position of theelement disposed on the receiving surface of the acoustic wave detector1105, and information on sensitivity and directivity. Conditions foracquiring an acoustic wave signal, such as imaging parameters to acquirethe acoustic wave, are also included in the acoustic wave signalinformation.

If an acoustic wave is detected by the photoacoustic wave signalmeasuring unit 1100 by moving the probe, the scanning region where theprobe detected the acoustic wave is handled as a reception region, andthe position of an element which detected the acoustic wave is handledas an element position in the reception region. In this case, thephotoacoustic wave signal information includes a position of thereception region in a coordinate system inside the apparatus, and anelement position in the reception region. The photoacoustic wave signalinformation also includes information on control of the light source,and information on compression of the object, as the conditions foracquiring an acoustic wave signal.

For the acoustic wave signal included in the photoacoustic wave signalinformation, the received acoustic wave signal may be transmitteddirectly, or may be transmitted after correcting the sensitivity of theelement or the gain. If irradiation of light and detection of theacoustic wave signal are repeated a plurality of times for a sameposition in one imaging process, the average value of the detectedacoustic signal values may be transmitted. Even if the probe is moved, avalue of the acoustic wave signal detected by an element having a samecapability as the previous element at the same position in the receptionregion may be included in the values to determine the average value.

Of the photoacoustic wave signal information, information that can beregarded as a statistical constant in the embodiment may be stored in amain memory 102 or magnetic disk 103 of the information processing unit1000 in advance, and be read and used when the image is reconstructed.Information that is dynamically determined each time an image isphotographed, on the other hand, is transmitted from the photoacousticwave signal measuring unit 1100 to the information processing unit 1000every time. For example, a position of an element on a receiving surfaceof the acoustic wave detector 1105 can be stored in the informationprocessing unit 1000 in advance.

The information processing unit 1000 acquires an instruction on theimaging from the user, determines an acoustic wave measurement methodconsidering the image quality of the reconstructed image, and instructsimaging to the photoacoustic wave signal measuring unit 1100. Theinformation processing unit 1000 also performs three-dimensional imagereconstruction processing using the photoacoustic wave signalinformation received from the photoacoustic wave signal measuring unit1100, and displays the image.

The functional blocks of the information processing unit 1000 will nowbe described. The information processing unit 1000 includes an imaginginstruction information acquiring unit 1001, a reconstruction methoddetermining unit 1002, a photoacoustic wave measurement methoddetermining unit 1003, a photoacoustic wave measurement methodinstructing unit 1004, a photoacoustic wave signal information acquiringunit 1005, and a reconstruction processing unit 1006. The informationprocessing unit 1000 further includes a data generating unit 1007, adata recording unit 1008, a data acquiring unit 1009, a data analyzingunit 1010, a display information generating unit 1011, and a displayunit 1012.

The imaging instruction information acquiring unit 1001 acquires aninstruction on imaging that the user inputs via an input unit 106. Theinstruction on imaging is, for example, information to specify animaging region in the acoustic wave signal measuring unit 1100, orinformation to specify an image quality of the reconstructed image.

A method for specifying an imaging region is, for example, the userspecifying only a two-dimensional region on a compressing plate of anobject, and determining a rectangular parallelepiped imaging regionbased on the thickness of the object measured by the photoacoustic wavesignal measuring unit 1100. Another possible method is informationprocessing unit 100 storing a region, specified in the coordinate systemin the photoacoustic wave signal measuring unit 1100, as presetinformation, and specifying an identifier of the region.

An example of information to specify the image quality of thereconstructed image is the number of acoustic wave signals used for thereconstruction processing. The number of acoustic wave signals used foreach point in the reconstruction region, or a relative detectionposition for each point of the acoustic wave signal, which is requiredfor each point, may be specified. The detection position of the acousticwave signal may be specified as an effective acoustic wave signal. Acondition may be set under which acoustic wave detection signalsassemble at all the element positions on the reception region, which canbe included in the range of directivity of the element of the probe.

These conditions on the acoustic wave signal can limit the degree of anartifact and bias. Furthermore, depending on the reconstructionalgorithm, parameters may be set according to the characteristics of thereconstruction algorithm or the acoustic characteristics of anenvironment in which the acoustic wave is detected, or the receptionconditions may be added. For the user to input the conditions, the usermay select an image quality level where these conditions are preset inadvance.

The imaging instruction information acquiring unit 1001 acquires imaginginstruction information from the user, and transmits the information tothe reconstruction method determining unit 1002.

Using the imaging instruction information and information on imagequality, the reconstruction method determining unit 1002 determines anappropriate reconstruction method based on the capability of thephotoacoustic wave signal measuring unit 1100, and the capability of thereconstruction processing unit 1006 which are stored in advance. Thereconstruction method determining unit 1002 generates reconstructioninstruction information based on the determined reconstruction method,and transmits the information to the reconstruction processing unit1006. The reconstruction method determining unit 1002 transmits thereconstruction instruction information and the imaging instructioninformation to the photoacoustic wave measurement method determiningunit 1003. The imaging instruction information may be directlytransmitted from the imaging instruction information acquiring unit 1001to the photoacoustic wave measurement method determining unit 1003.

Examples of the reconstruction instruction information are informationon a reconstruction region which corresponds to an imaging region, andinformation on parameters of reconstruction processing, such as areconstruction algorithm, and the number and pitch of voxels (unitregion, pixels in the case of two-dimensional data) to be reconstructed.If the acoustic wave measurement environment and reconstructionprocessing in an imaging region cannot be handled in a same processing,the imaging region may be segmented into a plurality of reconstructionregions, and a separate reconstruction instruction information may begenerated for each region.

The photoacoustic wave measurement method determining unit 1003determines an acoustic measurement method of the photoacoustic wavesignal measuring unit 1100 based on the acquired reconstructioninstruction information and the imaging instruction information. Forexample, setting information related to irradiation light control, suchas parameters on the light source and the optical path, is determined.

When signals are acquired in a wide range by scanning with a probe, thephotoacoustic wave measurement method determining unit 1003 calculates ascanning region, which is required for reconstructing the image usingthe instructed reconstruction method for the instructed imaging region,from the imaging instruction information and the reconstructioninstruction information. In this case, the scanning region is normallyone surface of the rectangular parallelepiped to be photographed, butthis is not always the case.

The photoacoustic wave measurement method determining unit 1003 alsodetermines a pitch of an element position in the reception region.Further, the photoacoustic wave measurement method determining unit 1003may determine parameters for the acoustic wave acquiring conditionsrelated to the image quality of the reconstruction processing, and amethod for correcting a signal.

The photoacoustic wave measurement method determining unit 1003generates acoustic wave measurement information integrating theinstruction information required for measuring these acoustic wavesignals, and transmits the acoustic wave measurement information to thephotoacoustic wave measurement method instructing unit 1004. In thisembodiment, the acoustic wave measurement information is generated foreach photography process, but acoustic wave measurement informationcreated in advance may be selected, and the identifier thereof may betransmitted.

The photoacoustic wave measurement method instructing unit 1004transmits the acoustic wave measurement instruction information to thephotoacoustic wave signal measuring unit 1100 to instruct the acousticwave measurement. The acoustic wave measurement instruction informationitself may be transmitted or an identifier thereof may be transmitted.

The photoacoustic wave signal information acquiring unit 1005 receivesthe photoacoustic wave signal information from the photoacoustic wavesignal measuring unit 1100, and transmits the photoacoustic wave signalinformation to the reconstruction processing unit 1006. Thephotoacoustic wave signal information acquiring unit 1005 also transmitsinformation on the irradiation light to the imaging region to the datagenerating unit 1007.

The reconstruction processing unit 1006 generates a three-dimensionalreconstructed image (volume data) for each point in the imagereconstruction region, using only the selected acoustic wave signals. Inother words, the reconstruction processing unit 1006 performsreconstruction processing using the photoacoustic wave signalinformation according to the reconstruction instruction information. Theimage reconstruction processing may be a time domain method or a Fourierdomain method only if a three-dimensional image is reconstructed basedon the analysis solution. Thereby a three-dimensional image thatindicates optical characteristic value distribution (initial soundpressure distribution and absorption coefficient distribution derivedtherefrom) inside the object can be generated, and the difference ofcomposition inside the object can be displayed. Light intensity may becorrected at this time.

If the setting of the reconstruction region and reconstructionparameters need be changed or corrected because the photoacoustic wavesignal measuring unit 1100 failed in the acoustic wave measurement, forexample, the change or correction can be executed at this time. Ifinformation on the acoustic wave measurement executing state is includedin the photoacoustic wave signal information, the necessity ofcorrection can be determined by comparing this information with thereconstruction instruction information.

The reconstruction processing unit 1006 transmits the generatedreconstructed image to the data generating unit 1007.

The data generating unit 1007 generates recording data based on thereconstructed image received from the reconstruction processing unit1006, and the information on photo-irradiation onto the imaging regionacquired from the photoacoustic wave signal information acquiring unit1005.

The recording data is generated by attaching information on thephoto-irradiation to volume data for each voxel (unit region). The dataformat that can be used is DICOM (Digital Imaging and Communications inMedicine), which is a standard for medical imaging. Information on thephotoacoustic diagnostic apparatus is not included in the standardspecification, but data can be handled easily without redundancy, whilemaintaining versatility of volume data if information onphoto-irradiation is stored in private tags. Thereby such generalfunctions as image display and analysis according to the capability ofthe viewer corresponding to the DICOM image can be used. If a viewercorresponding to information on photo-irradiation is used, the displayand analysis of information on the photo-irradiation can be performedusing a same data file.

The data generation unit 1007 transmits the generated recording data tothe data recording unit 1008.

The data recording unit 1008 stores the recording data in such a storagemedium as a magnetic disk 103 as a recording data file 1200. The storagemedium can be any type, and the recording data may be recorded by anexternal unit via a network.

The data acquiring unit 1009 acquires recording data from the recordingdata file 1200 to the information processing unit 1000, and transmitsthe recording data to the data analyzing unit 1010.

The data analyzing unit 1010 extracts a reconstructed image orinformation on photo-irradiation from the received recording data basedon the data format, and transmits the extracted information to thedisplay information generating unit 1011.

The display information generating unit 1011 generates the reconstructedimage and the display information based on the information onphoto-irradiation.

Image processing is performed on a reconstructed image if necessary. Forexample, if the reconstructed image is a three-dimensional image, suchas volume data, then volume rendering, multi-planar reconstruction ormaximum intensity projection, for example, is used. Image processing isperformed considering a brightness value that can be displayed on thedisplay screen. The reconstructed image based on the photo-irradiationmay be displayed integrating with other information.

Examples of the display information based on the information on theirradiation light are information on the direction of the light whichmakes it easier to identify the irradiation position of the light andthe irradiating surface, and information on the light intensity. A lineto represent the optical axis corresponding to the irradiation angle ofthe light may be generated and added to the display information. Variousdisplay information can be generated so that information is displayedbased on the information on the irradiated light, or analysis resultinformation is displayed.

The display information generating unit 1011 transmits the displayinformation to the display unit 1012.

The display unit 1012 is a display device for displaying the generateddisplay information, such as a graphic card, a liquid crystal display ora CRT display, and displays the display information transmitted from thedisplay information generation unit 1011.

The photoacoustic wave signal measuring unit 1100 and the informationprocessing unit 1000 may be integrated. A function to performmeasurement by a modality other than photoacoustic tomography (e.g.ultrasonic diagnosis) may be added to the apparatus configurationaccording to this embodiment.

FIG. 2 is a diagram depicting a basic configuration of a computer forimplementing the function of each component of the informationprocessing unit 1000 by software.

A CPU 101 controls each composing element of the information processingunit 1000. The main memory 102 stores a control program which the CPU101 executes, or provides a work area for the CPU 101 to executeprograms. A magnetic disk 103 stores an operating system (OS), a devicedriver for peripheral apparatuses, and programs to perform theprocessing in the flow chart, which is described later. A display memory104 temporarily stores display data for a monitor 105.

The monitor 105 is a CRT display or a liquid crystal monitor, forexample, and displays an image based on data from the display memory1204. An input unit 106 accepts pointing input from a mouse, or input ofcharacters from a keyboard by the operator.

An I/F 107 is for exchanging various data between the informationprocessing unit 1000 and external units, and is constituted by IEEE1394, USB and Ethernet® ports, for example. The data acquired via theI/F 107 is loaded to the main memory 102. The above composing elementsare communicably interconnected by a common bus 108.

FIG. 3 is a diagram depicting an example of the configuration of thephotoacoustic wave signal measuring unit 1100. This configurationimplements the photoacoustic wave diagnostic apparatus.

The light source 1101 is a light source of the irradiation light to anobject, such as a laser or a light emitting diode. For the irradiationlight, an irradiation light having a wavelength, at which the degree ofabsorption of the light by a specific component out of the componentsconstituting the object is expected to be high, is used.

The control unit 1102 controls the light source 1101, the opticalapparatus 1104, the acoustic wave detector 1105 and the positioncontrolling unit 1106. The control unit 1102 also amplifies an electricsignal of the photoacoustic wave acquired by the acoustic wave detector1105, and converts the analog signal into a digital signal. The controlunit 1102 also performs various types of signal processing and varioustypes of correction processing. The control unit 1102 also transmits theacoustic wave signal from the photoacoustic wave signal measuring unit1100 to such an external apparatus as the information processing unit1000 via an interface, which is not illustrated.

The control factors for the light source are, for example, the timing,waveform and intensity of laser irradiation. The control unit 1102 alsoperforms control to synchronize the signal detection by the acousticwave detector 1105 with the laser irradiation timing. The acoustic wavesignals of each element which are acquired by irradiating the laser aplurality of times may be added and averaged, so as to determine a meanvalue of the acoustic wave signals of each element.

The optical apparatus 1104 is, for example, a mirror to reflect light,or a lens to collect or expand light or to change the shape of light.The optical apparatus can be arbitrary only if the light 1103 emittedfrom the light source can be irradiated onto the object 1107 in adesired form.

A plurality of light sources 1101 and a plurality of optical apparatuses1104 may be disposed so that light is irradiated onto the imagingregions in various directions. The irradiated light from the lightsource 1101 may be propagated using such an optical wave guide asoptical fiber. If there is a plurality of light sources, an opticalfiber may be provided for each light source, or light from the pluralityof light sources may be propagated collectively by one fiber.

If the light 1103 generated by the light source 1101 is irradiated ontothe object 1107 via the optical apparatus 1104 under control of thecontrol unit 1102 in this configuration, the light absorber 1108 in theobject absorbs the light and emits the photoacoustic wave 1109. In thiscase, the light absorber 1108 corresponds to the sound source.

The acoustic wave detector 1105 is arbitrary only if an acoustic wavecan be detected, and examples are a transducer using the piezoelectricphenomena, a transducer using the resonance of light, and a transducerusing the change of capacitance. The acoustic wave detector 1105 maydirectly contact the object 1107 or may detect the photoacoustic wave1109 via a plate 1110 for compressing the object.

In the acoustic wave detector used in this embodiment, a plurality ofelements are two-dimensionally arrayed. By using such two-dimensionallyarrayed elements, an acoustic wave can be detected simultaneously at aplurality of locations, detection time can be decreased, and theinfluence of vibration of the object, for example, can be reduced. Anacoustic impedance matching agent, such as gel or water, may be usedbetween the acoustic wave detector 1105 and the object, so as tosuppress the reflection of the acoustic wave.

Here the photo-irradiation region on the object and the acoustic wavedetector 1105 may be movable. To move the photo-irradiation region, amovable mirror is used as the optical apparatus 1104 or the light sourceitself is mechanically moved, for example. The position of the acousticwave detector 1105 can be moved by the position controlling unit 1106.An example of the position controlling unit 1106 is a mechanism to movethe acoustic wave detector 1105 on the plate 1110 by a motor based onthe information of the position sensor.

The position of the photo-irradiation region and the position of theacoustic wave detector 1105 are synchronously controlled by the controlunit 1102. Thereby light can be irradiated over a wide range, and thephotoacoustic wave can be detected by the acoustic wave detector whichis located in an appropriate position with respect to the irradiationregion. The control unit 1102 also generates information on theirradiation light to the imaging region.

To move the probe, any moving method can be used only if an acousticwave signal detected by an element at each position on the receptionregion can be regarded as the acoustic wave signal detected by the probewhich positioned the element in this position. For example, if theelement surface of the probe is rectangular, the probe is moved for asize of the vertical width or the horizontal width of the rectangle at atime, and is stopped at each position after the move, and an acousticwave is detected there, that is using a step and repeat method. Bymatching the detection signal at each position, the same effect as usinga large sized probe can be implemented. The measurement may be performedwhile continuously moving the probe.

In this embodiment, an acoustic wave required for reconstructing animage in an imaging region specified by the user via the input unit 106is acquired. The imaging region is a three-dimensional region specifiedat each imaging process, within a region where the object can bephotographed based on the specification of the imaging apparatus.

The method for inputting the imaging region is arbitrary. For example,the coordinates of each vertex of a rectangular parallelepiped to be theimaging region may be inputted, or a mathematical formula to indicatethe imaging region, may be inputted. The imaging area may be specifiedby the user, specifying a rectangular region by mouse on an image of theobject which is photographed by a camera via a transparent plate, andmeasuring the depth of the object (thickness from the plate) in theregion. The imaging region need not always be a rectangularparallelepiped.

The processing procedure of this embodiment will now be described withreference to the drawings and the flow charts in FIG. 4 to FIG. 12.According to this embodiment, the imaging processing is executed for aspecified imaging region, conditions of the irradiation light used forthe reconstructed image are stored, and the stored data is utilized.

FIG. 4 is a flow chart depicting a procedure when the informationprocessing unit 1000 determines the reconstruction method and thephotoacoustic wave acquiring method after the user has inputted anoperation for imaging, and transmits the determined methods to thephotoacoustic wave signal measuring unit 1100.

The flow chart in FIG. 4 starts with the following state. First anoperator (technician) secures an object (e.g. breast of an examinee)with a holding plate, then sets parameters on imaging and image qualityvia the input unit 106, and instructs the start of imaging.

In step S401, the imaging instruction information acquiring unit 1001acquires setting information on the imaging and setting information onthe image quality as the imaging instruction information. Then theimaging instruction information acquiring unit 1001 transmits theacquired imaging instruction information to the reconstruction methoddetermining unit 1002. An example of the imaging instruction informationis the imaging parameters on the imaging region and the photoacousticwave acquisitions. An appropriate photo-irradiation method may beautomatically set by the imaging apparatus, instead of being set by theuser. The intensity and angle of the laser are set within a range thatthe apparatus can process. Information on an acoustic wave signalrelated to the image quality can also be set.

In step S402, the reconstruction method determining unit 1002 determinesa reconstruction method based on the imaging instruction information andthe pre-stored information on the photoacoustic wave signal measurementby the photoacoustic wave signal measuring unit 1100.

Here the information on the photoacoustic wave signal measurement isinformation on the photoacoustic wave signal measuring capability. Forexample, concerning a photographable region, information on the positionand size of the photographable region, a region where the probe can bescanned, and a range of the region where the laser can be irradiated areincluded in this information. Concerning irradiation light, suchinformation as the number of irradiated beams, wave length, intensity(density distribution), angle of irradiation light that can becontrolled, signal processing capability of the probe, such as movingvelocity and acoustic wave acquisition capability, and laser irradiationinterval are included.

The reconstruction method determining unit 1002 determines areconstruction method that can be executed with the specified imagequality when the imaging region included in the imaging instructioninformation is the reconstruction region. The reconstruction method tobe determined includes algorithms and parameters of the reconstructionprocessing. A correction method (e.g. light distribution correction),which is additionally executed, can also be determined.

In step S403, a reconstruction region for which reconstructionprocessing is performed during imaging is calculated. Normally theimaging region becomes the reconstruction region. However in some cases,the imaging region and the reconstruction region are different. Forexample, when both the sufficient imaging region and the image qualitymust be implemented, or when the capability of the apparatus isinsufficient for the required conditions, such as the reconstructionalgorithm types and parameters, the imaging region and thereconstruction region are different. In order to decrease thereconstruction processing time and to decrease the time of the entireimaging processing, a region of which image quality is obviously poormay be eliminated from the reconstruction region. The reconstructionmethod determining unit 1002 generates information for specifying thecalculated region as information on the reconstruction region.

In this embodiment, a case when the boundary surface where the lights ofthe imaging region and the reconstruction region are irradiated matcheswith the boundary surface of the object will be described. If the insideof the object is specified as the imaging region, however, theirradiation light that reaches the imaging region is determined bycalculating the transmitted scattering of light inside the object. Inthis case, the transmitted scattering in the biological tissue iscalculated based on the energy distribution of Gaussian scattering, andthe result is regarded as information on the irradation of light at eachposition on the boundary of the reconstruction region.

The reconstruction method determining unit 1002 transmits the determinedinformation on the reconstruction method and reconstruction region tothe reconstruction processing unit 1006 and the photoacoustic wavemeasurement method determining unit 1003.

In step S404, the photoacoustic wave measurement method determining unit1003 determines a method for controlling the photoacoustic wavemeasuring unit 1100 required for acquiring an acoustic wave in thegenerated reception region, and generates this method as information onphotoacoustic wave acquisition. For example, a method for scanning theprobe and a method for controlling irradiation of the light aredetermined. The photoacoustic wave measurement method determining unit1003 transmits the information on photoacoustic wave acquisition to thephotoacoustic wave measurement method instructing unit 1004.

Now a relationship between the irradiation light and the imaging region,which is determined by the information on photoacoustic wave acquisitiondetermined by the photoacoustic wave measurement method determining unit1003, based on the imaging region specified by the user, will bedescribed with reference to FIG. 5.

In FIG. 5, an object 501 which is a part of an examinee is secured tothe imaging apparatus. The reference numeral 502 is a holding plate, andis also the scanning surface of the probe. An acoustic wave, refractionof light and decay are generated depending on the thickness of thescanning surface 502. Since all of these do not have influence onessential points of explanation, they are not described in detail here.The holding plate 503 sandwiches the object 501 with the scanningsurface 502, and holds the object 501, and the holding plate 503 and thescanning surface 502 correspond to the plates 1110 in FIG. 3. By usingthe holding plate 503, the boundary of the imaging region and theboundary of the biological tissue can be approximately matched.Furthermore, light intensity can be calculated easily since the boundarybecomes a plane.

The reference numeral 504 denotes a space between the scanning surface502 and the holding plate 503. The depth of the photography regionviewed from the scanning surface can be calculated by measuring thespace 504. The shape and size of the object, the imaging region, and thethree-dimensional position of the imaging region can be specified by anarbitrary method. Any method, such as using a sensor that measures ashape and size, or a method of deriving the shape and size from a cameraimage by image processing, can be used, as long as the imaging regionand the reconstruction region can be specified and associated with theinformation on the irradiation light in the apparatus.

The probe 505 constitutes the acoustic wave detector 1105, and detectsan acoustic wave by moving on the scanning region of the scanningsurface. The reference numeral 506 denotes the height of the scanningregion of the probe, that is, a height of the scanning region in thevertical direction in FIG. 5. The height 506 is determined from theregion on the reception surface, which is a part of the controlparameters calculated by the photoacoustic wave measurement methoddetermining unit 1003.

The scanning region need not always match with the size of the boundarysurface of the imaging region. This depends on the range of the voxelsto be constructed, from which the photoacoustic wave required for thereconstruction processing is acquired. Depending on this setting, thescanning region could be slightly larger or slightly smaller than theimaging region.

The reference numeral 507 denotes a normal line to the boundary surfaceof the imaging region on the side to which the irradiation light 508 isirradiated. If the imaging region and the reconstruction region match,this normal line is also a normal line to the boundary surface of thereconstruction region. An incident angle 509 of the light with respectto the imaging region corresponds to an incident angle of the irradiatedlight with respect to the boundary surface of the reconstruction region.The incident angle 509 may be constant depending on the specification ofthe optical apparatus 1104. However if the relative positionalrelationship between the imaging region and the optical apparatus 1104changes as shown in FIG. 5, the incident angle changes depending on theirradiated light.

The reference numeral 510 denotes a distance between the holding plate503 and an emitting spot of the optical apparatus 1104. The distance 510changes depending on the compressing state by the holding plate 503,even if the position of the emitting spot to emit the irradiation lightof the optical apparatus 1104 and emission angle are determined. As aresult, if a diffused light is used as the irradiation light, forexample, the size of the irradiation surface on the imaging region maychange according to the distance 510. It is preferable that the holdingplate 503 has a high light transmittance. The incident angle of theirradiation light is determined considering the refraction of light whenthe light transmits through the holding plate.

The imaging region 511 is a region which the user specifies in theimaging instruction information. The photoacoustic wave measuring unit1100 controls the photo-irradiation position and the probe position sothat the reconstructed image of the imaging region 511 can be acquired.The number of times of photo-irradiation and photoacoustic waveacquisition, positions, directions and the number of rays which areirradiated at the same time can be determined in various ways accordingto the reconstruction methods or the like.

Here description with reference to FIG. 4 continues. In step S405, thephotoacoustic wave measurement method instructing unit 1004 generatesacoustic wave measurement instruction information based on theinformation on the photoacoustic wave acquisition, and transmits theacoustic wave measurement instruction information to the photoacousticwave measuring unit 1100. The acoustic wave measurement instructioninformation is constituted by commands and parameters to instruct thephotoacoustic wave measuring unit 1100 to acquire an acoustic wave, forexample.

By the above described procedure, processing when the informationprocessing unit 1000 determines the reconstruction method and thephotoacoustic wave acquisition method, and transmits the determinedmethods to the photoacoustic wave measuring unit 1100, can beimplemented.

FIG. 6 is a flow chart depicting the processing procedure when thephotoacoustic wave measuring unit 1100 executes photoacoustic wavemeasurement, generates photoacoustic wave signal information, andtransmits the photoacoustic wave signal information to the informationprocessing unit 1000. This flow starts with the information processingunit 1000 receiving the acoustic wave measurement instructioninformation transmitted from the photoacoustic wave measurement methodinstructing unit 1004 of the information processing unit 1000.

In step S601, the photoacoustic wave signal measuring unit 1100determines the control parameters to control the optical apparatus 1104and the acoustic wave detector 1105. Examples of the control parametersare each irradiation position in the imaging region, the number of timesof irradiation to a same position, irradiation timing, wave length andintensity (or density distribution). If a plurality of laser beams canbe used, the control parameters of the irradiation light, such as typeof laser beam, are determined. For the control of the acoustic wavedetector 1105, control parameters for detecting a photoacoustic wave,such as a position of the probe, timing of the acoustic wave measurementand time, are determined. Control of the photoacoustic wave measurementand determination of control parameters are executed by the control unit1102 based on the acoustic wave instruction information transmitted fromthe information processing unit 1000.

In step S602, the control unit 1102 detects an acoustic wave whilesynchronizing the photo-irradiation position and the probe position, andrecords data that is required for reconstructing the imaging region.

In step S603, information on the irradiation light to the imaging regionis generated. This information includes both apparatus-specificinformation on the irradiation light which is converted so that thisinformation can be handled relative to the imaging region, andinformation on the irradiation light which need not be converted. Forirradiation position, direction and irradiation region of the light,position information on the coordinate system of the imaging region isgenerated.

If the irradiation light is diffused light, the size of the irradiationregion changes as the distance 510 changes. For example, the focusedspot radius of a Gaussian beam is normally given by Expression (8). Thisindicates that if a distance from the light emitting spot changes, therelative position with the beam waist (focal distance) changes, and theirradiation region size changes accordingly.W=λf/πW ₀  (8)where W is a spot diameter, W₀ is an incident light radius,λ is a wavelength, and f is a focal distance.

The size of the irradiation region can be measured using the reflectionon the boundary surface of the imaging region, for example. The distance510 and the size of the irradiation region may be provided in advance asa data table for each apparatus.

The incident angle of each irradiation light (angle formed by theoptical axis and the normal line 507) is also generated on thecoordinate system of the imaging region. For the light intensity, notthe intensity at irradiation, but the intensity after the lighttransmitted through the holding plate 503 and decayed, is recorded asthe intensity value or light density distribution. This information onthe angle and intensity are included in the information on theirradiation light to the imaging region, and stored for each irradiationlight. Information that is not different for each irradiation light,such as information on the wavelength and type of laser and the numberof times of irradiation at a same position, are also stored together.

In this embodiment, information on the irradiation light is generatedafter the acoustic wave is measured, but the irradiation lightinformation for the imaging region may be generated each time light isirradiated. In this case, the processing in step S602 and the processingin step S603 are repeated each time light is irradiated for measuring anacoustic wave. If a measuring apparatus, such as an optical sensor, isused, the intensity and incident angle of the irradiation light thatreached the imaging region can be accurately measured.

In FIG. 5, the boundary surface of the imaging region (or reconstructionregion) matches with the surface of the holding plate. Therefore thelight that enters the imaging region is appropriately unchangedirradiation light, even if slight refraction or the like is generated bythe holding plate. However if the imaging region (or reconstructionregion) exists inside the object, as in the case of reference numeral701 in FIG. 7, the light intensity distribution factor must bedetermined by estimating the light energy distribution, consideringscattering and absorption. In this case, Expression (9), to determinethe energy distribution of Gaussian scattering, for example, can beused. Then as information on the irradiation light to the imagingregion, luminous flux, when the boundary surface of the imaging regionis the cross-section, is calculated at each position of the boundarysurface of the imaging region, based on the calculated light energydistribution.P(θ)=P ₀ exp[(−½)·(θ/σ)²]  (9)where P(θ) is a luminous intensity or radiance in the θ direction, P₀ isluminous intensity or radiance in a specular direction, and σ is astandard deviation of Gaussian distribution.

When measurement of the acoustic wave ends, the control unit 1102generates photoacoustic wave signal information in step S604. Thephotoacoustic wave signal information is information on an acoustic wavesignal which the probe detected at each position on the scanning surface502, and information on the irradiated light. If an acoustic wave signalis detected a plurality of times at a same position, a mean value or arepresentative value may be used. The information on the acoustic wavesignal includes information on acoustic wave acquiring conditions fordetecting an acoustic wave signal, or for determining an acoustic wavesignal value.

In step S605, the photoacoustic wave signal measuring unit 1100transmits the generated photoacoustic wave signal information to theinformation processing unit 1000.

By the above mentioned procedure, the acoustic wave acquiring unit 1100measures the acoustic wave, and transmits the photoacoustic wave signalinformation to the information processing unit 1000.

FIG. 8 is a flow chart depicting a procedure when the informationprocessing unit 1000 executes the reconstruction processing based on thephotoacoustic wave signal information transmitted from the photoacousticwave signal measuring unit 1100, and stores the recording data. The flowchart in FIG. 8 starts with the photoacoustic wave signal informationacquiring unit 1005 receiving the photoacoustic wave signal informationfrom the photoacoustic wave signal measuring unit 1100.

In step S801, the photoacoustic wave signal information acquiring unit1005 transmits the acquired photoacoustic wave signal information to thereconstruction processing unit 1006 and the data generating unit 1007.Only the information on the irradiation light to the imaging region maybe extracted and transmitted to the data generating unit 1007.

In step S802, the reconstruction processing unit 1006 performsreconstruction processing based on the received photoacoustic wavesignal information, and information on the reconstruction method and thereconstruction region transmitted from the reconstruction methoddetermining unit 1002, and generates the reconstructed image data of theimaging region. The reconstructed image data is generated, for example,as volume data that corresponds to the position and size of the imagingregion. The reconstruction processing unit 1006 transmits thereconstructed image data to the data generating unit 1007.

In step S803, the data generating unit 1007 generates information on theirradiation light to the reconstructed image data, associating thereconstructed image data acquired from the reconstruction processingunit 1006 and the information on the irradiation light to the imagingregion. To generate the recording data, DICOM image data, for example,is generated, and information on the irradiation light is checked andrecorded in private tags. RAW data of the reconstructed image may begenerated in an arbitrary format, with associating the size, typeinformation or the like of this RAW data.

When information on the irradiation light for the reconstructed imagedata is generated, such information as the position of the irradiationlight on the irradiation surface and the incident angle of theirradiation light is converted into coordinates in the voxel space ofthe volume data. Then the result is converted into a format that can beeasily applied to the volume data. For example, if information on theirradiation light is too detailed compared with the pitch of the voxelof the volume data, the information is converted into a level matchingthe pitch of the voxel.

Now the positional relationship of the information on the irradiationlight with respect to the reconstructed image data will be describedwith reference to a plurality of examples. FIG. 9 is a case when theimaging region is small, and the photo-irradiation position is only onelocation on the irradiation surface 902. The reference numeral 901denotes volume data, the reference numeral 902 denotes an irradiationsurface of light, the reference numeral 903 denotes a normal line, thereference numeral 904 denotes an incident angle θ, and the referencenumeral 905 denotes an optical axis of the irradiation light. In thiscase, information on the irradiation light for the reconstructed imagedata is information on the irradiation light to one irradiationposition. If the irradiation light is emitted to a same position for aplurality of times, information for each irradiation light may bestored, or a mean value may be stored.

FIG. 10 is a case when the imaging region is large, and thephoto-irradiation position exists on a plurality of irradiation surfaces1002. The reference numeral 1001 denotes volume data, the referencenumeral 1002 denotes an irradiation surface of the light, the referencenumeral 1003 denotes a normal line, the reference numeral 1004 denotesan incident angle θ, and the reference numeral 1005 denotes an opticalaxis of the irradiation light. This corresponds to a case of acquiringan acoustic wave at each location during movement, while scanning theprobe and the photo-irradiation position. In this case, information on aplurality of irradiation lights is generated for the volume data, andincident angle, intensity and shape of the irradiation surface areindividually recorded for each irradiation light.

If the space between the actual photo-irradiation positions is smallenough for the reconstructed image processing, information on theirradiation light may be simplified when the recording data isgenerated. For example, when reconstruction is possible only if theirradiated boundary surface of the volume data and the generalirradiation direction are known, the information can be simplified.

FIG. 11 shows an example of combined irradiation surfaces. The referencenumerals 1001 to 1005 are the same as FIG. 10. The combined region 1106of the irradiation surface is a region when the plurality of irradiationsurfaces 1002, which corresponds to the plurality of photo-irradiationpositions, is combined. This region is the boundary surface on thecoordinate system of the volume data. Based on the intensity andincident angle of each irradiation light, one representative value (e.g.mean value) is generated and used as data on the irradiation light tothe reconstructed image.

If such processing as averaging and simplification is performed wheninformation on the irradiation light to the imaging region is convertedinto information on the irradiation light to the reconstructed image, anidentifier of the type of information on the irradiation light to thereconstructed image is also included in the recording data.

In FIG. 11, the irradiation light is irradiated only to one boundarysurface, but may be irradiated onto a plurality of boundary surfaces.For example, if light is also irradiated from the opposite side of theobject simultaneously, light intensity in the imaging region increases,and an image with high contrast can be acquired.

The data generating unit 1007 transmits the recording data, in which thereconstructed image data and information on the irradiation light to thereconstructed image are recorded, to the data recording unit 1008.

In step S804, the data recording unit 1008 stores the recording datagenerated by the data generating unit 1007 to a storage medium.

A procedure to display a reconstructed image using information on theirradiation light stored in the recording data will be described withreference to the flow chart in FIG. 12. The flow chart in FIG. 12 startswith the information processing unit 1000 reading the recording datafrom the recording data file 1200.

In step S1201, the data acquiring unit 1009 reads the recording datafrom the recording data file 1200, and transmits the recording data tothe data analyzing unit 1010.

In step S1202, the data analyzing unit 1010 extracts the reconstructedimage data and the information on the irradiation light to thereconstructed image, including an identifier of the type of theinformation from the recording data, and transmits the extractedinformation to the display information generating unit 1011.

The display information generating unit 1011 generates display imageinformation of the reconstructed image, that can be displayed on thedisplay unit 1012, using the reconstructed image data. For example, ifthe reconstructed image is displayed by MPR (Multi-PlannerReconstruction), the cross-sectional image of the reconstructed imageand the boundary line of the region divided based on the quality of theimage are superposed and displayed. An image acquired by volume rendingcan also be displayed. Color and graphics may be added so that theirradiated boundary surface of the reconstructed image is distinguishedfrom the other boundary surfaces, and the influence of the light can berecognized more easily.

Graphics to be added to the display image may be changed depending onthe type of the information on the irradiation light. For example, ifinformation on the irradiation light is simplified, an arrow markindicating the direction of the light may be added, and if theinformation on the irradiation light is provided for each irradiationposition, information on the shape of the irradiation surface and theoptical axis may be added for each position. If the intensity of theirradiation light is displayed as color-coded depending on the level,the relationship of the color and intensity can be displayed by a graphor color bar. Furthermore, information other than an image, such asdescription using text, based on a pixel value of each position of athree-dimensional reconstructed image, that is a voxel value of volumedata, may be displayed.

Further, the quality of decay, intensity or the like of the light in thereconstructed image may be understood and displayed. Such informationcan be estimated by a shape and size of the irradiation surface, anincidence angle, an intensity value (or light density), a wavelength, ascattering coefficient of the object among other factors. Thereby theuser can understand a region where the intensity of the irradiationlight is sufficient and a region where this intensity is not sufficient,and the difference of image quality can be recognized.

If volume rendering is performed, it becomes difficult for the user tounderstand a region where image quality is different, because the imageis rotated three-dimensionally, and apparatus information during theimaging process is lost. In such a case, display image information,where graphics and annotation are added to make it easier to recognize aregion influenced by the irradiation light for the reconstructed image,can be easily attached without recording or analyzing redundant datathat depends on the imaging apparatus.

If a region in the object which interrupts propagation or scattering oflight can be determined based on the distribution of the lightabsorption coefficients in the reconstructed image, this information maybe displayed. For example, a region where the shadow of the irradiationlight is generated in the reconstructed image or a region where thescattering of the light is not uniform can be displayed. If theinformation can be used as an input value for calculating other analysisdata, like the case of calculating oxygen saturation from thereconstructed image to indicate the initial sound pressure distributionof a photoacoustic wave, the accuracy of the analysis result improves byconsidering the quality of the conditions of the irradiation light inthe reconstructed image using the information on the irradiation light.

The display information generating unit 1011 transmits the generateddisplay information to the display unit 1012. The display unit 1012displays the received display information. By the procedure describedabove, the recording data is read and the reconstructed image can bedisplayed using the stored information on the irradiation light.

In this embodiment, the photoacoustic wave signal measuring unit 1100generates the information on the irradiation light to the imagingregion, and the information processing unit 1000 generates informationon the irradiation light to the reconstructed image. However thephotoacoustic wave signal measuring unit 1100 may generate informationon the reconstruction region. The information processing unit 1000,rather than the photoacoustic wave signal measuring unit 1100, maygenerate the information on the irradiation light to the imaging region.The data generating unit 1009 may perform the calculation on scatteringof the transmitted light inside the object.

The photoacoustic wave measurement method determining unit 1003 may beintegrated with the photoacoustic wave measuring unit 1100. Further, animaging apparatus in which the information processing unit 1000 and thephotoacoustic wave signal measuring unit 1100 are integrated may beused. The information processing unit 1000 comprising only the dataacquiring unit 1009, the data analyzing unit 1010, the displayinformation generating unit 1011 and the display unit 1012, out of theabove mentioned components of the information processing unit 1000, mayaccess the recording data file 1200.

According to the apparatus configuration and procedure described above,display image information considering the influence of the light in thereconstructed image, and recording data that can be used for calculatingthe analysis result can be provided without using a special format, andwithout the cost of using an enormous amount of apparatus-specific data.Furthermore, standard volume data can be acquired, therefore a standardviewer and analysis software can be used, and recording data which isless restricted by application can be generated and used.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2012-158988, filed on Jul. 17, 2012, which is hereby incorporated byreference herein in its entirety.

The invention claimed is:
 1. An object information acquiring apparatuscomprising: at least one CPU; and a memory, wherein the at least one CPUand the memory cooperate to function as: a processing unit configured togenerate a DICOM image data representing characteristic information onan object based on an acoustic wave generated from the object which hasreceived irradiation light; a data generating unit configured togenerate a recording data including information of the irradiation lightand the DICOM image data representing the characteristic information;and a data outputting unit configured to output the recording data to adata recording unit configured to record the recording data, and whereinthe information of the irradiation light is at least one of intensity ofthe irradiation light, a wavelength of the irradiation light, anirradiation position of the irradiation light, an irradiation angle ofthe irradiation light, an irradiation frequency of the irradiation lightand an irradiation region of the irradiation light, and the informationof the irradiation light is associated with the DICOM image datarepresenting the characteristic information based on the acoustic wavegenerated from the object which has received irradiation light.
 2. Theobject information acquiring apparatus according to claim 1, wherein theinformation of the irradiation light is associated with the DICOM imagedata representing the characteristic information using a tag.
 3. Theobject information acquiring apparatus according to claim 2, wherein theprocessing unit segments the object into a plurality of unit regions,and generates the DICOM image data representing the characteristicinformation for each unit region, and the data generating unit generatesthe recording data by storing the information of the irradiation lightin the tag and attaching the tag to the DICOM image data representingthe characteristic information for each unit region.
 4. The objectinformation acquiring apparatus according to claim 1, wherein theinformation of the irradiation light includes information of an angle ofthe irradiation light with respect to the object.
 5. The objectinformation acquiring apparatus according to claim 1, wherein theinformation of the irradiation light includes information of wavelengthof the irradiation light.
 6. The object information acquiring apparatusaccording to claim 1, wherein the information of the irradiation lightincludes information of a number of times photo-irradiation is executed.7. The object information acquiring apparatus according to claim 3,wherein the processing unit determines information on an image qualityin each of the unit regions based on the information of the irradiationlight included in the recording data and causes a display unit todisplay the DICOM image data with the information on the image quality.8. An object information acquiring method comprising: a step ofgenerating a DICOM image data representing characteristic information onan object based on an acoustic wave generated from the object which hasreceived irradiation light; a step of generating a recording dataincluding information of the irradiation light and the DICOM image datarepresenting the characteristic information; and a step of outputtingthe recording data to a data recording unit configured to record therecording data, wherein the steps are performed by at least a CPU andmemory acting in cooperation to perform the steps, and wherein theinformation of the irradiation light is at least one of intensity of theirradiation light, a wavelength of the irradiation light, an irradiationposition of the irradiation light, an irradiation angle of theirradiation light, an irradiation frequency of the irradiation light andan irradiation region of the irradiation light, and the information ofthe irradiation light is associated with the DICOM image datarepresenting the characteristic information based on the acoustic wavegenerated from the object which has received irradiation light.
 9. Theobject information acquiring method according to claim 8, wherein theinformation of the irradiation light is associated with the DICOM imagedata representing the characteristic information using a tag.
 10. Theobject information acquiring apparatus according to claim 2, wherein theprocessing unit is configured to generate the DICOM image datarepresenting the characteristic information in a reconstruction region,the data generating unit generates the recording data by storing theinformation of the irradiation light at a boundary surface of thereconstruction region in the tag and attaching the tag to the DICOMimage data representing the characteristic information in thereconstruction region, and the processing unit reads the recording datafrom the data recording unit and causes a display unit to display theDICOM image data with the information of the irradiation light at theboundary surface of the reconstruction region.
 11. The objectinformation acquiring apparatus according to claim 4, wherein theprocessing unit causes a display unit to display the DICOM image datawith a line to represent an optical axis corresponding to the angle ofthe irradiation light based on the recording data.
 12. The objectinformation acquiring apparatus according to claim 1, wherein theinformation of the irradiation light includes an intensity of theirradiation light in the object, and wherein the processing unit causesa display unit to display the DICOM image data with color-codingdepending on the intensity of the irradiation light based on therecording data.
 13. The object information acquiring apparatus accordingto claim 1, wherein the processing unit causes a display unit to displaythe DICOM image data representing the characteristic information on theobject with the information of the irradiation light based on therecording data.
 14. The object information acquiring method according toclaim 8, further comprising: a step of displaying the DICOM image datarepresenting the characteristic information on the object with theinformation of the irradiation light based on the recording data. 15.The object information acquiring apparatus according to claim 1, whereinthe data generating unit transmits the recording data to an externaldata recording unit as the data recording unit via a network.
 16. Theobject information acquiring apparatus according to claim 1, furthercomprising: a light source; and an acoustic wave detector comprising atleast one detection element, configured to detect the acoustic wavegenerated by irradiating the object with irradiation light from thelight source and output a signal, wherein the processing unit generatesthe DICOM image data representing the characteristic information byusing the signal output from the acoustic wave detector.
 17. The objectinformation acquiring method according to claim 9, further comprising: astep of segmenting the object into a plurality of unit regions, whereinthe DICOM image data representing the characteristic information foreach unit region is generated, and wherein the recording data isgenerated by storing the information of the irradiation light in the tagand attaching the tag to the DICOM image data representing thecharacteristic information for each unit region.
 18. The objectinformation acquiring method according to claim 17, further comprising:a step of determining information on an image quality in each of theunit regions based on the information of the irradiation light includedin the recording data, and a step of displaying the DICOM image datawith the information on the image quality.
 19. The object informationacquiring method according to claim 9, further comprising: a step ofdisplaying the information of the irradiation light, wherein the DICOMimage data representing the characteristic information in areconstruction region is generated, wherein the recording data isgenerated by storing the information of the irradiation light at aboundary surface of the reconstruction region in the tag and attachingthe tag to the DICOM image data representing the characteristicinformation in the reconstruction region, and wherein the information ofthe irradiation light at the boundary surface of the reconstructionregion is displayed based on the recording data.
 20. The objectinformation acquiring method according to claim 8, further comprising: astep of displaying the DICOM image data with a line to represent anoptical axis corresponding to an angle of the irradiation light based onthe recording data, the information of the irradiation light includinginformation of the angle of the irradiation light with respect to theobject.
 21. The object information acquiring method according to claim8, further comprising: a step of displaying the DICOM image data withcolor-coding depending on an intensity of the irradiation light in theobject based on the recording data, the information of the irradiationlight including the intensity of the irradiation light in the object.22. The object information acquiring method according to claim 8,wherein the recording data is transmitted to an external data recordingunit as the data recording unit via a network.
 23. The objectinformation acquiring method according to claim 8, wherein theinformation of the irradiation light includes information of an angle ofthe irradiation light with respect to the object.
 24. The objectinformation acquiring method according to claim 8, wherein theinformation of the irradiation light includes information of wavelengthof the irradiation light.
 25. The object information acquiring methodaccording to claim 8, wherein the information of the irradiation lightincludes information of a number of times photo-irradiation is executed.